Field of the Invention
The present invention relates generally to endoscopic image capture units, and more particularly to image capture units mounted in a distal tip of an endoscope.
Description of Related Art
Typically, endoscopes used in minimally invasive surgery come in various tip angles. Two common tip angles are a zero degree angle and a thirty degree angle. A schematic diagram of a portion of an endoscope 100 with a zero degree tip angle is presented in FIG. 1A. An endoscope with a zero degree tip angle is referred to as a zero degree endoscope. A schematic diagram of a portion of an endoscope 110 with a thirty-degree tip angle is presented in FIG. 1B. An endoscope with a non-zero degree tip angle is referred to as a non-zero degree endoscope.
Typically, a stereoscopic endoscope used in minimally invasive surgery includes two optical channels, which are identical in construction. Thus, the portion of the optical channel illustrated in FIGS. 1A and 1B is the same in both channels of a stereoscopic endoscope.
Objective lens system 120 in endoscope 100 includes some of the same lenses as in objective lens system 130, i.e., lens 101A is the same as lens 101B, lens 102A is the same as lens 102B, lens 103A is the same as lens 103B, and lens 104A is the same as lens 104B. However, objective lens system 130 in endoscope 110 also incorporates a prism 131, which directs the line of sight at the desired angle. As used herein, a prism refers to a transparent solid body that refracts light (i.e., changes the direction of light passing through the transparent solid body). As used herein, a substantially flat piece of glass that is not configured to refract light is not a prism
To facilitate the interchangeability of endoscopes 100 and 110 in a teleoperated surgical system, the optical path length of objective lens system 120 is kept the same as the optical path length of objective lens systems 130. Thus, to compensate for the optical path through prism 131 in objective lens system 130, it is necessary to insert a block of glass 121 in objective lens system 120. The optical path length through block of glass 121 is the same as the optical path length through prism 131.
Thus, each endoscope with a different angled tip requires a different prism. If an endoscope family includes an endoscope with a zero degree tip (FIG. 1A), an endoscope with a thirty-degree tip (FIG. 1B), and an endoscope with a forty-five degree tip (not shown), three different objective lens systems must be manufactured and assembled so that each objective lens system has the same optical path length through the system.
While the optical path lengths of objective lens systems 120 and 130 are the same, light traveling through objective lens system 130 incurs two mirror bounces that light traveling through objective lens system 120 does not incur, i.e., the optical path in objective lens system 130 is folded, while the optical path in objective lens systems 120 is non-folded. The two mirror bounces slightly degrades the image captured using endoscope 110 relative to the image captured using endoscope 100.
Typically, endoscopes 100 and 110 have an outer diameter of 12 mm or 8.5 mm. Consequently, prism 131 is quite small and requires careful, costly, manufacturing.
Also, thirty-degree prism 131 has to be aligned to the other optics precisely. One challenge of this thirty-degree design is that, in a stereoscopic endoscope, the alignment of the right and left eyes requires that the objective lens assemblies in the right and left channels be rotationally aligned so the thirty-degree directions for the right and left channels are pointing in exactly the same direction. While the issues associated with an angled tip endoscope are known, the approach still has been to use an appropriate prism in the endoscope to achieve viewing through the angled tip.